This is the U.S. national phase of International Application No. PCT/JP00/04200 filed Jun. 27, 2000.
The present invention relates to a method for manufacturing a multilayer circuit board, and more particularly to a method for manufacturing a flexible multilayer circuit board having a hollow terminal portion and the like formed in an internal layer.
This type of multilayer circuit board may have a configuration requiring a terminal portion for a connector terminal and the like to an internal layer circuit board owing to circumstances of a wiring pattern. As such a primary configuration, there is a flexible multilayer circuit board provided with a terminal portion in a cable portion thereof. In general, gold plating or solder plating is performed to such a terminal portion.
If electrical conduction can be attained to the terminal portion after laminating an external layer circuit board on the internal layer circuit board, there is no problem. However, if such mutual conduction can not be achieved, plating must be carried out at the stage of forming a wiring pattern on the internal layer circuit board.
However, since the terminal portion of the internal layer circuit board must be exposed on the surface eventually, it is preferable to laminate the external layer circuit board corresponding to the terminal portion as a window, but there are processes such as wiring patterning of the external layer circuit board, erosion of the gold coating or the solder coating as well as through hole plating after the laminating process.
Under the present situation, the external layer circuit board is laminated in the window configuration such that the terminal portion of the internal layer circuit board is provided to the external layer circuit board, and the terminal portion must be masked in each of stages of through hole plating or etching. In such a case, an adhesive tape having the chemical resistance is generally used for the masking process, but the process may be troublesome because the tape must be attached each time. Further, there may occur such a problem as that the tape can be peeled off during the process.
It is, therefore, an object of the present invention to provide a method for manufacturing a flexible multilayer circuit board characterized in that an external layer copper-clad laminate is directly used as a masking material in order to efficiently achieve masking with respect to the terminal portion of the internal layer circuit board without adopting masking means such as a tape described above.
To achieve this aim, the present invention provides a method for manufacturing a flexible multilayer circuit board comprising the steps of: producing an internal layer circuit board to which a required wiring pattern is formed so as to provide a opening portion at a predetermined position and expose a terminal portion to the opening portion; laminating a single-sided copper-clad laminate through each interlayer adhesive layer to which another opening portion is provided on both sides of the internal layer circuit board at a position corresponding to a position of the opening portion; previously forming two slits piercing the single-sided copper-clad laminate at corresponding positions placed outside from edges of the opening portion by a predetermined distance in accordance with opposed two sides of the opening portion; forming a required wiring pattern with respect to a conductive layer of each single-sided copper-clad laminate; and finally punching out the single-sided copper-clad laminate at a position including respective both ends of the two slits to take off unnecessary removal pieces, thereby exposing the opening portion of the internal layer circuit board including the terminal portion.
Here, the internal layer circuit board can be formed by a single-sided copper-clad laminate or a double-sided copper-clad laminate. Further, it is preferable that the slit is formed at a corresponding position placed outside from the edge of the opening portion by a distance of 0.2 mm to 1.0 mm. Moreover, as the interlayer adhesive layer, a material which also has a surface protection layer for the wiring pattern formed to the internal layer circuit board can be used.